Hyperkeratosis Penetrans (Kyrle's Disease)

Kyrle,¹in 1916, described an unusual dermatosis in a young woman (Fig. 1). The lesions primarily involved the extremities, axillae, and thorax. Early lesions consisted of pinhead-sized, slightly elevated, follicular papules resembling keratosis pilaris. Older lesions were bean-sized, elevated, bright brown papules with a central scale. In some areas there were polycyclic, hyperkeratotic plaques. Removal of the heavy scales and crusts from the plaques revealed discrete, crateriform papules topped by central depressions into which fitted conical, keratinous plugs. Healing of the lesions after the cornified plugs were extracted resulted in a slight, pigmented depression. Histologically, the early lesions revealed a moderate hyperkeratosis, concentrated in thick lamellated plugs situated in the ostia of hair follicles and sweat glands. The prickle-cell layer revealed acanthosis, disordered cell arrangement, and alterations in the cells themselves. Older lesions showed a thinning of the prickle-cell layer due to pressure from the cornified plugs, which eventually